Hot-rodding the Toyota MGR

[thingstodo]

Originally Posted by freebeard

.. so I calculate less than 1200 as it sits.

Wow - nice and light!

With the Beetle, I'd like the primary battery pack to replace the rear seat, with a secondary pack in front replacing the gas tank sized for front/rear weight balance. And an option to plug-in an additional battery where the engine used to reside, or in a trailer, to extend the range. Minimum range would be a 3 mile track plus return road. There's always a wait in line between runs.

3 miles is pretty low. I would expect multiple runs on a charge.

I'm assuming a DC-DC inversion, for instance a 1st/2nd gen Prius battery at 288 volts bumped to 650.

Good - that makes fewer cells and less space. BUT it likely means lower amps for your race, which would then be a slower time.

But EV-Power | CALB (40Ah-400Ah) shows $55-60 per, or $11,520 for 192 each. Is that right?

Yes - that pack would likely give you a range of 100 miles in normal driving. Batteries cost a lot. But the 400A would be nice at 650V for your racing.
At 288V you would need 90 cells. That's still $5400 plus straps.

The racing setups I have read about (I have not seen any in person) use smaller capacity cells like A123 pouch cells (20 ah, 20C max discharge) to get a lot of power in a short time with a limited range. That does not work so well with a multi-function vehicle.

Edit: used+Prius+battery+pack into Google returns pricing in the range $1760-2628, with one site offering "...from $850". So that's my default choice. Dimensions are 15 x 40 x 9 in. I can't measure the back seat width right now but it's 42" at the rear window. So I could stack two or three there.

Using 288V instead of 650V gives you a lot more choices.

What's a headway cell? There is an access plate at the front of the center tunnel that's about 1 1/2x3". If I could slide 6ft long sticks in there in pairs it might hold six.That would be 92 cells right below center of gravity. That might present cooling problems though.

Headway is just a brand name. Like Panasonic or CALB. Headway are used more in the RC helicopters and scooters. They are a cylindrical cell, like a extra-large D cell .. at least that's the type I've seen pictures of.

6 feet of cells, 38 mm (1.5 inch) in diameter, screwed together (they apparently have threaded holes in each end) would give you 13 in a stick * 3.2V = 41.6V. 288V would need 7 sticks.

Figuring out which cells you can use to make good use of your available space, get the voltage output you want, and be economical, is a challenge ... you will likely have some trade-offs.

[freebeard]

The racing setups I have read about (I have not seen any in person) use smaller capacity cells like A123 pouch cells (20 ah, 20C max discharge) to get a lot of power in a short time with a limited range. That does not work so well with a multi-function vehicle.

It will be multi-functional. I would hope to do something like start with two Prius packs on their last legs to get it rolling and then upgrade to more/better/newer as opportunity presents itself. There are more build phases, the electic conversion is only the first (then suspension and wheelbase changes, blow everything apart for refinishing, wheels & tires, interior/zombie proofing).

The area below the rear seat cushion contains the stock battery on one side and the voltage regulator on the other; a volume about equal to four stock batteries. It could be filled with pouches. Once again low and right at the center of gravity.

Do you know if Paul's controller is amenable to mixing battery types, and differing voltage inputs?

[thingstodo]

Originally Posted by freebeard

Do you know if Paul's controller is amenable to mixing battery types, and differing voltage inputs?

Paul's controller is battery agnostic. If the battery pack supplies current, Paul's controller will use it. There is a voltage range (that I can't locate right now). To drive 650V I believe a few capacitors had to be changed out? Not sure on the low end - about 48V, perhaps?

I think you would need to be careful mixing battery chemistries for different reasons. The charge curves are, I believe, different. So the charger used for a NiMH pack would expect the charge curve to rise at different points than a LiFePO4 cell. I expect the charge to terminate using different rules as well.

That assumes that the packs are in parallel. If they are in series, I think you would need separate chargers as well ... but that's a guess.

In series, you would be limited to the max current of the lowest-rated pack and the amp-hours of the lowest capacity pack.

[freebeard]

Thanks.

I can see the problems with differing battery types, and I guess any given battery presents a variable output. Maybe there are battery types that play nice together.

I was thinking of using the high discharge rate battery like a supercapacitor.

If you double the voltage into a DC-DC inverter, is the output volatge clamped or does it rise?

[thingstodo]

Originally Posted by freebeard

I was thinking of using the high discharge rate battery like a supercapacitor.

That *SHOULD* work. The batteries that can supply high current, do that. The lower current batteries 'top up' the high current batteries after the acceleration is done. This is what I have read - I have no experience with this topic.

If you double the voltage into a DC-DC inverter, is the output volatge clamped or does it rise?

Paul would be a better person to comment. The voltage doubler (or tripler or whatever) will have a maximum output dependent on component values.

I don't think the output is clamped.

[e*clipse]

I guess I'll chime in here.

It's generally known as not a good idea to mix & match cells. Even to the extent of mixing old/new batteries of the same type. Why? they will have different discharge curves and the pack will be limited by the worst performer of your batteries. Even different ages of the same cell will have different discharge curves. Expecting similar performance from cells with different characteristics will lead to many grey hairs. If you are entertaining the idea of mixing Lithium with Nickle-Metal Hydride or Lead Acid, you will be mixing different discharge curves and different start/end charging voltages. How you would (or some BMS) keep track of that - on the fly - is a mystery to me.

For example, I have a lithium powered LED flashlight, using two of the same cells the Tesla pack is made of (the 18650 laptop cell) in series. I purchased a large amount of these cells to build a test battery management system. So, being cheap, I grabbed two of the cells that had already been cycled many times and sat for several years. One was pretty worn out, the other pretty new. Long story short, the total run time of the flashlight is limited to the run time of the worn-out cell. The flashlight's LED system limits power output depending on incoming voltage. When the worn-out cell hits the "fall-off" point of its discharge curve, it shuts down the whole system, even though the other cell is more than half full. At one point, the run time of the flashlight was pathetic, worse than your average "c" cell powered incandescent bulb flashlight. Solution? replace the worn-out cell with one comparable to the stronger cell. Way better performance/run time.

Yes, I'm describing a simple flashlight, but the same thing will happen when you mix cells for something big like a car pack.

To make things worse, cycleing the worn out cell heavily like that will cause it to fail prematurely, unless you have a BMS that individually monitors cells, and takes care of the weak cell.

*Edit*
Also, regarding voltage doublers: They put out the same POWER ( minus the efficiency loss ) as the input power. Say you have a 250V pack. The motor you have is 50kW and wants to be supplied with 500V. The efficiency of the voltage doubler is 95%. (I'm just pulling #'s out of my ***. ) So, using the doubler will result in a 5% loss: 50kW * 5% = 2.5kW.... Therefore, the power being supplied by the pack must be 52.5kW. Of course, there are other losses for the inverter, wiring, etc - but we're focusing only on the doubler. Power = I*V . Therefore the current being supplied to the inverter by the doubler is 50kW/500V = I = 100Amps . The trick is that the doubler is not a constant current device, it is a constant power device. Therefore, the current that must be supplied by the batteries is 52.5kw (taking doubler losses into account). 52.5kW/250V = 210Amps. So, in drag racing the bug, theoretically you can run just as fast as with a high voltage pack, you will just be demanding 2X (or whatever) the current from the lower voltage battery pack.

A question, why are you interested in, say a prius pack (or battery pack) vs individual cells? Certain cells, like the headway are set up for being easy to inter-connect. Others can be a royal PIA, requiring welding the cells together.

- E*clipse

[freebeard]

I know it will get complicated at some point, but I'd like to see soft switches on the power board that can configure it for pre-programed battery combinations for clip-on packs or trailered pusher/generator.

The donor car is in it's space, up on jack stands with the wheels removed. As soon as I can show a picture of the MGR correctly positioned on the floor jack, I'll feel like I can start a build thread. I may start with shrouding the whole thing in 6mil polyethlene so I can sandblast the firewall, wheelwells and framehead.

e*clipse -- or is it E*clipse? We were just making conversation to keep the thread active.

I'm pretty agnostic. Like Neil Blanchard, I'm counting on something new popping up just before I have to lay the money down. The wood-tin battery sounded promising. And the fractal graphene anode. Or just Tesla flooding the market.

Frankly the reason I'm leaning toward Prius is that the battery pack (or at least one model) is 15x7x40. That is close to the size of a Beetle's rear seat cushion. Two laid longitudinal on either side of the center tunnel (below and behind the seats) and a third one where the seat cushion was, and it's done. There exists a reburbishment market.

Also I've been reading about how Toyota use three packs, charged in series, but drawn down only two of the three at a time. They undercharge to extend battery life and leave headroom for regen. And the battery packs have their own integrated charger system. [all forgoing subject to me having gotten it right]

Edit: I had an opportunity to compare the MGR drive flange with the drive flange on a VW transaxle. The Lexus part has four studs on a 4" circle, VW uses six threaded bolt holes on a 3" circle. So my hope now is that a 3/4" thick steel plate adapt disk (similar to adapters for mismatched wheel lugbolts) will work. By my math there's a little more than an inch between holes on the two circles. It may require Allen head bolts, but that would save needing custom axle work.

[few2many]

Eagerly waiting to see what you guys come up with. This was discussed in other forums, but never went anywhere. He you though about rewinding for lower voltage? Maybe changing the pattern from wye, to delta?

[freebeard]

Could you provide links to those other forum threads?

My understanding, as far as it goes, is that FOC benefits from deriving the C-phase from the A- and B-phase[s]. Not sure how that would affect or be affected by a delta configuation.

My plan is to advance the state of the art for electric Beetle conversions from the current DC boat anchor/lead-acid battery paradigm. So I'm contemplating an unmodified MGR and a bolt-in installation. So far the original front transmission to the front of the MGR looks to be the biggest hurdle. Simplest would be to bolt or weld a new crossmember into the sheet metal.

I hope to find that a shrouded cooling fan will be sufficient; else, like e*clipse intends, it will be drilled and tapped for an external oil cooler.

[few2many]

Run a cooler, it would be more worth it. Check DIY electric car forum for the MGR. Check Ivan's garage forum for info on rewinding to lower voltage. Going from wye to delta will half the voltage.